This invention relates to the triggering of ignition pulses in spark-fired internal combustion engines. It is especially adapted for use in two-stroke outboard marine engines.
A necessary requirement of operation for spark-fired internal combustion engines is a spark that is delivered to the right cylinder at the right time to ignite the combustion of a mixture of fuel and air. For many years, such a spark was provided by a set of breaker points which interrupted the current flow in an inductor that represented a primary winding of a step-up transformer. The high-voltage impulse that was thus generated was distributed to cylinders by a rotating mechanical switch that effected a direct electrical connection individually to each cylinder. The timing sequence was thus the result of a wiring sequence, and the operating necessity for varying the timing of a spark with respect to top dead center (TDC) of the pistons in the cylinders was accomplished by making the breaker and switching arrangement rotatable.
The system described above led to the development of radio-frequency interference as a result of the spark produced at the breaker points by interrupting the flow of current. The breaker points themselves were subject to pitting as a result of the interruption, and the rotating switches that distributed current to the cylinders were also subject to corrosion that led to insufficient sparking and a need for repairs.
An early attempt at improving the operating of ignition systems involved replacing the breaker points with a silicon-controlled rectifier (SCR) to provide arcless switching. Other attempts have included using an alternator to time the spark as well as generate energy for it.
Two patents showing ways of generating a spark without the use of breaker points are U.S. Pat. No. 3,669,086, "Solid State Ignition System," and U.S. Pat. No. 3,942,501, "Timing Circuit for flywheel Ignition System." U.S. Pat. No. 3,669,086 generates high-energy pulses for ignition by attaching be permanent magnet to the flywheel and rotating the permanent magnet past a charge-trigger coil assembly to charge a capacitor. The trigger coil then receives an impulse from the rotating magnet to trigger the discharge of the capacitor into ignition coils. The magnet that rotates with the flywheel is the principal source of energy for the spark, in addition to controlling the timing. In contrast, U.S. Pat. No. 3,942,501 produces individual triggering impulses for each of a pair of cylinders by having a fixed coil for each pair of cylinders. Each fixed coil has an armature that spans a segment of the rotating magnet structure of an alternator that has exposed magnet faces producing one alteration of sign in each direction once per revolution. The signal is used only for triggering, and not as the source of ignition energy. The systems of both of the patents cited above have the disadvantage that they are not readily adapted to control ignition for a large number of cylinders. The '501 patent teaches two cylinders, for which it uses seven magnet segments, and triggering more cylinders would require an increased number of magnet segments. The '086 patent teaches the firing of four spark plugs, but they are fired in groups of two, with each spark plug intended to fire once per cycle in the power stroke and once per cycle in the exhaust stroke of a four-stroke cycle. Each of these modes of operation represents a disadvantage that is overcome by the circuit of the present invention.
A third way of avoiding the use of breaker points to generate and control ignition impulses is disclosed and claimed in U.S. Pat. No. 4,269,152, entitled "Breakerless Pulse Distribution System and Opto-Electrical Distributor Therefor." In this patent, a shutter in the form of a cup with an opening is caused to rotate about an array of phototransistors. A shutter in the cup permits the coupling of light from a light-emitting diode (LED) to the phototransistor to initiate the timing of a spark. This patent teaches the advantages of pulsed LEDs, in contrast to the disadvantages of using such a timed shutter With a continuous light source. However, the use of a rotating-cup shutter requires a mechanical adjustment to change the ignition angle.
In each of the patents described above, each cylinder receives an impulse directing the spark from a dedicated line. A simpler ignition system can be achieved if one line is caused to have a firing impulse for each cylinder, which is the processed in an electronic module to distribute the Associated spark to the proper cylinder. However, such a system requires some unambiguous method of identifying a particular cylinder so that the timing of the spark is not changed by one or more entire spark intervals. This is characterized as selecting a number one cylinder.
Proper operation of an internal combustion engine requires variation in the timing of the spark with respect to top dead center (TDC), which is normally taken as the reference for timing a spark. Timing that is optimum to start an engine is typically different from the optimum timing for a running engine. A cold engine may call for a different spark timing from the setting required when the engine is warm. In addition, it is also desirable to increase the idling speed of a cold engine to minimize the chances of stalling the engine. For any given speed of an engine, the optimum timing is typically a function of the load on the engine. One way of sensing the load on the engine is to detect the throttle position. The changes in timing that are described above have generally been accomplished in the past using a mechanical spark distribution system in which the spark timing as changed mechanically.
It is an object of the present invention to provide a better means for timing sparks in an internal combustion engine that is spark-ignited.
It is an object of the present invention to provide an improved ignition system having a single line for input into an electronic ignition system in which the single line carries a timing pulse for each cylinder.
It is a further object of the present invention to provide an improved means of identifying a particular cylinder to control the timing of the ignition.
Yet another object of the present invention is to provide an improved ignition system which uniquely provides cylinder identification and ignition trigger signals, and which includes a computing means for varying the timing of the trigger signals as a function of operating characteristics of the engine.